1. Field of the Invention
The invention relates to a vertical Hall effect sensor comprising a semiconductor crystal having a pair of current electrodes arranged on its surface and having a Hall effect voltage contact arranged between the current electrodes, wherein the semiconductor crystal has sufficient thickness to allow a current flow between the current electrodes in the semiconductor crystal, which current flow makes the Hall effect sensor sensitive to a magnetic field aligned parallel to the surface.
The invention also relates to a brushless electric motor having at least one Hall effect sensor and having a permanent magnet, wherein the permanent magnet is connected to the motor shaft such that they rotate together, and the Hall effect sensor is arranged opposite this permanent magnet, and wherein the electric motor has at least three coils.
2. Description of the Prior Art
A vertical Hall effect sensor is disclosed in U.S. Pat. No. 4,987,467. Vertical hall effect sensors are integrated Hall effect sensors and have the advantage of being sensitive to a magnetic field parallel to the chip surface. Such Hall effect sensors are used in particular for accurate measurements of magnetic fields. A further Hall effect sensor is known from the article xe2x80x9cA CMOS-compatible 2-D vertical Hall magnetic-field sensor using actice [sic] carrier confinement and post-process micromachiningxe2x80x9d by Paranjape et al. in Sensors and Actuators A, Volume A53, No. 1/03, May 1996 (1996-05), pages 278 to 282, XP000620310. This is a traditional 2-D Hall effect sensor, in which two Hall effect sensors are arranged in a cruciform shape with respect to one another such that they can use a common central contact.
Known, conventional Hall effect sensors are also used for controlling electric motors. A corresponding brushless electric motor with the associated controller is known from the article xe2x80x9cEffects of Software Speed-Control Algorithm on Low-Cost Six-Step Brushless DC Drivesxe2x80x9d by S. Ellerthorpe in Power Conversion-and-Intelligent Motion, Volume 22, No. 1, pages 58 to 65 (January 1996). Another brushless electric motor, which uses three separate Hall effect sensors, is known from U.S. Pat. No. 3,988,654.
In the said motor, three Hall effect sensors, which each cover 180xc2x0 of a circular disk parallel to the permanent magnet, are arranged with an offset of 120xc2x0 to one another so that the voltages produced by these Hall effect sensors result in a three-bit feedback signal which defines the rotor position with respect to six 60xc2x0 areas. The information relating to this is used in IP, PI and PPI controllers to achieve a constant speed from the electric motor.
These motors have the disadvantage that the corresponding systems which carry out the control algorithms have a space requirement that severely limits the capabilities to miniaturize the motors. The arrangement of the Hall effect sensors in respect to one another is difficult with regard to the aligned planarity and with regard to the accurate alignment of the angles.
Against the background of this prior art, the invention is based on the object of designing a vertical Hall effect sensor of the type mentioned initially such that it allows better angular resolutions to be achieved, and in particular such that three Hall effect voltages, respectively shifted through 120xc2x0, can be produced when a rotating magnetic field is applied.
A further object of the invention against the background of the said prior art is to design an electric motor equipped with a vertical Hall effect sensor such that this electric motor can be configured as a micromotor with as small a space requirement and as simple actuation as possible.
The first-mentioned object is achieved according to the invention for a vertical Hall effect sensor of the type mentioned initially in that the Hall effect sensor has three or more arm sections which are arranged at equal angular intervals from one another and which run together in a central section, in that each arm has an outer current electrode which is arranged opposite a central inner current electrode in the central section, with these current electrodes in each case forming the said pair of current electrodes, and in that a Hall effect voltage contact is arranged between the respective outer current electrodes and the central inner current electrode to allow a current flow between the current electrodes in each arm section of the semiconductor crystal, which current flow produces a number of output signals from the Hall effect sensor (for a magnetic field aligned parallel to the surface) corresponding to the number of arms and with an appropriately predetermined angle dependency.
Since various arms each form a complete Hall effect sensor, the Hall effect sensor can be made sensitive in a very accurate manner to different angles of the magnetic field in the plane of the crystal surface. The integrated design results not only in excellent accuracy with regard to the angles of the sensors to one another due to use of the same crystal surface, but also in sensitivity for the same components of the magnetic field.
The further object according to the invention is achieved for an electric motor of the type mentioned initially in that the Hall effect sensor is a vertical Hall effect sensor according to the invention having at least three arms, in that the number of arms corresponds to the number of coils so that at least three Hall effect voltages which are phase-shifted with the same phase interval between one another can be produced by the vertical Hall effect sensor when the motor shaft is rotating, which Hall effect voltages can be supplied after amplification to the coils as a power signal.
The use of the vertical Hall effect sensor according to the invention in a brushless electric motor allows very simple circuitry to be achieved for this electric motor, and this is highly advantageous for miniaturization of the overall unit.
Further advantageous embodiments are characterized in the respective dependent claims.
The invention will now be described in detail using various exemplary embodiments of the invention and with reference to the attached drawings.